_read_write
static int _read_write(int hdev, void *bufw, void *bufr, int cbrw, int lsb);
err = _read_write(hdev, pw, pr, icount, popt->lsb);
err = _read_write(hdev, pw, NULL, popt->count + popt->ncmd, popt->lsb);
err = _read_write(hdev, pw, pr, icount, popt->lsb);